Dewaxing process



Jan. 19, 1954 J, E STORMENT 2,666,730

DEWAXING PROCESS Filed 001'.. 24, 1951 ATTORNEYS Patented Jan. 19, `1954 v to Phillips lgletroleum of. Delaware Company, a corporation Application OctobefrlZl, 195:1, Serial No. 252,956

aciaims. (c1. 19e- 18) -This `invention relates `to .dewaxing of hydrocarbon oils. In-one of its-aspects the :invention vis concerned Withmaintaining lter rates or Vthe restoration offlter rates Without lresort to ,exter-nal solvent or leven solvent as such/within the process.v f

' In the lsolvent dewaxing of .hydrocarbon oils, the ilter rate determines the .throughput of the plantand is therefore of the utmost importance. The lter rate is dependent primarily uponwax crystal Structure which in turn is affected by several factors such lasrnixing temperatures, chilling rates, solvent v:to oil ratio, the properties of the oil, etc. In many Ycases .crystal modiers are rused v to improve or modify the :Wax crystal structure so as to give a more porous nlter cake Vand 'thereby increase the filter rate.

.iFrequently, however, even when using crystal modifiers, the'lter rate Will decrease in ashort period of time to values iar below normal ,and in someextreme cases ltration practically stops. The cause of `these low lter ,rates is not always easily determined. Vin fact in someV cases With the sameoil stock, the same chilling rates, the

same solvent-oil ratios, :the-same filtering temx peratures :and apparently with theother operating conditions vthe same the lter'rate maybe normal at one time and below normal atanother. l ,Y

I have found that when these periods ofy 101W lter rate `occur for no apparent reason, the iilter-rate can be restoredzto normal values, .and frequently to valuesabove normal, by recycling aportionof ythe chilled lter feed back to some point in the system ahead of the `final Chiller. The amount to vbe recirculated varies and in most cases should be held to a .minimumsince each barrel of Amixture recirculated back sout a-barrel ofr fresh mixture. However, even under Lthese conditions, it is advantageous to use my .method of recirculation Whichwill restorethe-filter rate in a short period of time compared tothe .time required for the system .toright itself unalded. :in some "instances withlovv fllterrates, it has been necessary toshut down and completelyflush ,the system.` My method of recirculation eliminatiesV these difficulties.

The attached diagrammatic drawing illustrates anapplicationA of my .invention Wax .bearing 'charge oil from cl ,is ,passed through heater 2Y .where it isaheated to approximately V18o-210"luto destroy, the previous crystallinerhistory' of `the mx; From Y o.o5;,'co.41.43%VY of, a :crystal Lmodifier is added at -3 andfrom 0.6 to 3 volumes of propane per .wolume of .1 oil .is added `at-fll. f Theamount of crystal modier and propane used varies with the Aviscosity of thev waxy cil. The mixture is then passed through mixer 5 and heater 6' to insure thorough mixing. The mixture leaves heaters 6 at a temperature of approximately 175 F. and is passed through heat exchangers 'i Where 'it is cooled to r10G-115" F. and passed `'to Warm lsolution tank 8. 'From Warm solution tank -Sthe mixture flows to'chiller 9 :Where a vrreduction in pressure causes evaporation ofpart of the propane solvent and `the'solution is chilled-to -30 or 50 l?.V vPropane evaporated -in the Chillers 'is `replaced.bypropane from dry storage l(notshovvn) From filter `feed tank I0 ythe charge solution normally flows tothe lters (not shown). However in periods of lovv` lter -rate a portion of the charge solution is recirculated through line -r il and injected-into the system through one'. or more of -linesA l2, I3, Id, I5 or Ait -as desired.

Usually line SI5 Aisfthe preferred point of injection. Thus, it is especially noted,V as being important in lthe now preferred point of injection choice,-that, according Ato the invention, the cold filter feed is added to a relatively hct'stream of OiLzWhich may contain some propane, but which -in rthe drawing'described here doesnot contain propane, to cause'in said oil atan ele- .vated temperature locally an almost instantaneous or sudden'chilling. The amount circulated will vary :from 25 to 75 per cent of the Aoriginal charge solution.

. lExample I B./H. of a SAE 250iwax bearing lubeioil stock from a Mid-Continent crude oil was charged and heated as previously described to -200 F. 0.4% ofa-'crystalfmodiiier and 180 B /I-I. of propane Ywere added to give a total solution oi 270 B./H. The solution Was thoroughly mixed and heated to Y F. as described above.Y The solution was then cooled by heat exchange .to 118 F. and chilled rby' auto refrigeration 4to +40o F. at arate of approximatelyfl degrees per minute. The lterin'grate was l270 barrels .per hour. vThev solution was filtering normally when, Vfor someY reason,the lter ratedejcreased to .the point Whereonly 65B.'/H. of fresh oil Wafslbel ing charged. Recirculation of chilled solution to vthe system ahead -of the Ypropane-oil 4mixer Was started atfa rate of' approximately '65 Corresponding reductions were made in the amounts 'of freshf oil Aand propane'solvent Ibeingl charged. In-V making these .reductionstthe original solventtooil ratio .-.on ther .fresh mixture was maintained. During this recycling, op-

eration the temperature of the effluent from heater 6 was approximately 125 F. instead of approximately 165 F. prior to starting the recycle. Likewise the efliuent from heat exchangers l was approximately 105 F. instead of the 118 F. prior to starting the recycle. In approximately 40 minutes a definite improvement in filter rate was noted. After approximately Gflminutes, it was possible to start decreasing the amount of solution being circulated until at the end of approximately 90 minutes recirculation was stopped and the original filter rate, 270 BJH. of fresh solution was easily maintained.

From the example it is seen that the filter rate having dropped to 195 barrels per hour of fresh solution from 270 barrels per hour was re-established in about 60 minutes time, recirculation of the chilled filter feed could be stopped in 90 minutes and all this was done Without resort to external solvent or internal solvent as such. Indeed, it is surprising to find that recirculation of low filtering rate material, as described, would result in re-establishment of the original filter rate.

Eample II 115 B./H. of a SAE 20 wax bearing lube oil stock prepared from a mixture of West Texas and Mid-Continent topped crude oils by vacuum distillation, and phenol solvent extraction was charged and heated as previously described to 210 F. in order to destroy the previous crystalline history of the wax. 0.16 per cent of a crystal modifier and 150 B./H. of propane were added to give a total solution of 265 B./H. The solution was thoroughly mixed and heated to 151 F. by exchange with steam in the heater 6. The solution was cooled in heat exchangers l with cold dewaxed oil solution to 102 F. and then chilled by auto refrigeration to -35 F. at a rate of approximately 4 degrees per minute. The filter feed rate was 265 barrels per hour. The solution was filtering normally when for some reason the filter rate decreased to the point where only 68 B./H. of fresh oil was being charged. Recycle of chilled solution from the filter feed charge tank to a point in the system ahead of the propane-oil mixer, and prior to the point of clean propane solvent addition, was started at a rate of 91 BJI-I. Corresponding reductions were made in the amounts of fresh oil and propane solvent being charged. In making these reductions, the original solvent to oil ratio on the fresh mixture was maintained. During this recycling operation, the temperature of the effluent from heater 6 Was approximately 108 F. instead of the 151 F. prior to starting the recycle. Likewise the effluent from heat exchangers 'l was approximately 85 F. instead of the 102 F. prior to starting the recycle. In approximately 30-40 minutes a definite improvement in lter rate was noted. After approximately 60 minutes, it was possible to start decreasing the amount of solution being circulated until at the end of approximately 90 minutes recirculation was stopped and a filter rate of 213 B./H. of fresh solution was easily maintained. The fresh solution charge rate was not raised to its original value of 265 barrels per hour immediately following cessation of recycling because of a desire to observe the filtering characteristics of the fresh solution for a few hours prior to raising the charge. In this case, the filtering characteristics Were as good or better than before the ltering trouble occurred and the charge was raised after a few hours' operation.

Reasonable variation and modification are possible within the scope of the foregoing disclosure and the appended claims to the invention the essence of which is that by recirculating a portion of an improperly filtering chilled filter feed ina hydrocarbon oil dewaxing process to a point prior to the chilling step, preferably to a point prior to the addition of any solvent to the oil, while it is at an elevated temperature to cause locally therein a sudden chilling, the characteristics of the ultimately obtained chilled filter feed can be altered thus to maintain or to re-establish the original desired filter feed rate. It will be understood that according to the invention both intermittent and continuous recycle of chilled filter feed can be practiced in this manner to substantially avoid any loss of filter feed rate. Or,

as described, the recycling step of the inventionl can be practiced when some loss in filter feed rate has indicated that'something has gone wrong with the filtering characteristics of the wax.

It is not known just why the step which forms the basis of the present invention will maintain or restore desirable filter feed rates but it is clear that the invention is applicable to those situations of loss of filter feed rate which occur for no apparent reason when all other operating conditions remain the same as these were when satisfactory filter feed rates were being obtained. Finally, as stated, it is of importance to note that according to this invention the solution which is recycled is known to contain wax crystals apparently of such structure that they will not filter properly.

I claim:

1. In a hydrocarbon oil dewaxing operation in which the oil is mixed with a solvent and then chilled prior to a wax filtering operation and wherein the filter rate tends to decrease for no apparent reason, the step of causing normal desirable filter feed rate which comprises recycling a portion of the chilled filter feed to a point in the operation immediately preceding the admixture of solvent and immediately admixing said oil and filter feed mixture with solvent ahead of the chilling step.

2. A process according to claim 1 wherein the solvent is propane.

3. A process for dewaxing a wax bearing charge oil which comprises the steps of heating a wax bearing charge oil to a temperature sufficient to destroy its crystalline history, admixing said oil with a suitable solvent, cooling and chilling said solution, recycling a portion of said chilled solution to a point in the operation after said heating step and which is prior to the admixture of the said oil with said solvent, and filtering the remainder of said chilled solution.

4. A process according to claim 3 wherein the solvent is propane.

5. The dewaxing of an SAE 250 wax bearing lube oil stock obtained from a Mid-Continent crude oil which comprises heating said stock to a temperature of 200 F., adding a minor amount of a crystal modifier thereto, then adding propane in quantities sufficient to obtain complete solution upon reheating to a temperature of about F., cooling said mixture and then chilling by propane evaporation to about 40 F. at an approximate rate of 4 degrees per minute, ltering until the original filtering rate has decreased substantially, then recirculating some of the chilled filter material being filtered to a point in the operation after said lrst heating step but Yexperienced is about 65 barrels per hour (filter feed rate is approximately equal to 195 barrels per hour) and the quantity of chilled filter feed recirculated is approximately 75 barrels per hour.

1. The dewaxing of a SAE 20 wax-bearing lube oil ,stock obtained from a mixture of West Texas and Mid-Continent top crude oils by vacuum distillation and phenol solvent extraction which comprises heating said stock to a temperature of 210 F., adding a minor quantity of a crystal modifier thereto, then adding propane in quantities sumcient to obtain complete solution upon reheating to a temperature of 151 F., cooling said mixture and then chilling by auto refrigeration to a temperature of 35 F. at an approximate rate of 4 degrees per minute, filtering until the original filtering rate has decreased substantially,

then recirculating some of the chilled lter feed being filtered to a point in the operation after said rst heating step but ahead of the said admixture of said oil with the said propane and 6 continuing said recirculation until the original fllterrate has been established.

8. A process according to claim 7 wherein there is used for each 115 barrels of oil about 150 barrels of propane, the feed rate to the lter is about 265 barrels .per hour, and the lowering of said rate experienced is 108 barrels per hour (lter feed rate is approximately equal to 157 barrels per hour) and the quantity of chilled iilter feed recirculated is approximately 91 barrels per hour.

9. In the dewaxing of a hydrocarbon oil which has been prepared for a filtering operation and to which solvent has been added and the mixture of solvent and oil thus obtained has been chilled and which mixture apparently is suitable for ltration but which tends to be unsuitable for filtration at a proper filter feed rate, the step of cycling at least a portion of said unsuitable oil, as prepared for filtering, to the preparation for filtering operation.

JOSEPH E. STORMIEN'I.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A HYDROCARBON OIL DEWAXING OPERATION IN WHICH THE OIL IS MIXED WITH A SOLVENT AND THEN CHILLED PRIOR TO A WAX FILTERING OPERATION AND WHEREIN THE FILTER RATE TENDS TO DECREASE FOR NO APPARENT REASON, THE STEP OF CAUSING NORMAL DESIRABLE FILTER FEED RATE WHICH COMPRISES RECYCLING A PORTION OF THE CHILLED FILTER FEED TO A POINT IN THE OPERATION IMMEDIATELY PRECEDING THE ADMIXTURE OF SOLVENT AND IMMEDIATELY ADMIXING SAID OIL AND FILTER FEED MIXTURE WITH SOLVENT AHEAD OF THE CHILLING STEP. 